iOS (Jailbroken): iMessage has the handy feature that shows when someone is typing a message to you in the app, but it doesn't show up anywhere else in iOS. If you want to track when someone is typing a message to you from anywhere, TypeStatus and Predicter are both jailbreak tweaks that do just that.

Both tweaks do things a little differently. TypeStatus shows a simple little message bubble icon in your status bar when it detects someone is typing an iMessage. Predicter sends you an actual notification when the message starts. They're both handy in their own ways, and come in useful if you're getting ready to walk out the door and notice someone is typing a message to you.